This invention relates to a translator for measuring the amount of color correction for color printing, more particularly to a translator for correcting the spectral characteristics of projected light on the easel of a photographic enlarger for color printing, based on the amounts of color correction and exposure as determined for example by a negative color analyzer which measures these amounts only from the conditions of the negative, as well as on other additional conditions of which will virtually affect color prints such as those involved in the optical projecting system of the enlarger, color balance correction filter, etc.
In making color prints on an enlarger equipped with color balance correction filters, it has heretofore been practiced to select a combination of correction filters for a particular color negative such that the ratio of measured light intensities for the red, green and blue colors will be identical with the tricolor light intensity ratio previously determined by experiments and to determine the exposure time by measuring the intensity of light passing through the color negative with the selected filters set in position.
However, this method has to be practiced in the darkroom and the operations involved are very troublesome and inefficient inasmuch as changing one of the red, green and blue filters affects the outputs of the other two filters.
As disclosed in U.S. Pat. application, Ser. No. 135247 filed Apr. 19, 1971, we have already proposed an apparatus of the non-darkroom type for measuring the amount of color correction for color printing, namely a negative color analyzer, by which the light intensity measurement is conducted for the color negatives to automatically determine the amount of color correction and exposure time in an attempt to improve the above-mentioned complex and troublesome procedure which requires much experience. In fact, the proposed apparatus indicates the desired color correction filters and exposure time instantaneously and simultaneously.
However, since the negative color analyzer measures the amount of color correction and exposure time based only on the conditions of the negative, the information thereby provided does not include none of the changes in the conditions of the optical projecting system of the enlarger such as age of the light source, variations in the power source voltage, fading of the color correction filters, fluctuations in the transmission factors of the filters per se and difference in the amount of color correction attributable to the spectral transmission factor of the enlarger lens which differs from enlarger to enlarger. Consequently, if printing is conducted on the enlarger based on the foregoing information, the changes in the conditions of the projecting optical system and the like will adversely affect the quality of the image on the resulting color print.
Furthermore, its has been desired that the negative color analyzer be adapted for use with enlargers of both color additive type and color subtractive type and that, for use with enlargers of the subtractive type, a negative color analyzer adapted for correction with filters of a certain series, for example of Kodak series, be also adapted for used with an enlarger equipped with color correction filters of Agfa series.